Adoptive immunotherapy, which involves the transfer of autologous antigen-specific T cells generated ex vivo, is a promising strategy to treat viral infections and cancer. The T cells used for adoptive immunotherapy can be generated either by expansion of antigen-specific T cells or redirection of T cells through genetic engineering (Park, Rosenberg et al. 2011). Transfer of viral antigen specific T cells is a well-established procedure used for the treatment of transplant associated viral infections and rare viral-related malignancies. Similarly, isolation and transfer of tumor specific T cells has been shown to be successful in treating melanoma.
The current protocols for treatment of patients using adoptive immunotherapy is based on autologous cell transfer. In this approach, T lymphocytes are recovered from patients, genetically modified or selected ex vivo, cultivated in vitro in order to amplify the number of cells if necessary and finally infused into the patient. Autologous therapies face substantial technical and logistic hurdles to practical application, their generation requires expensive dedicated facilities and expert personnel, they must be generated in a short time following a patient's diagnosis, and in many cases, pretreatment of the patient has resulted in degraded immune function, such that the patient's lymphocytes may be poorly functional and present in very low numbers. Because of these hurdles, each patient's autologous cell preparation is effectively a new product, resulting in substantial variations in efficacy and safety.
Ideally, one would like to use a standardized therapy in which therapeutic cells could be pre-manufactured, characterized in detail, and available for immediate administration to patients. Such standardized therapy can be performed by using allogeneic cells obtained from individuals belonging to the same species but which are genetically dissimilar.
However, the use of allogeneic cells presently has many drawbacks. Endogenous TCR specificities of allogeneic cells recognize the host tissue as foreign, resulting in graft versus host disease (GvHD), which can lead to serious tissue damage and death. T cell receptors (TCR) are cell surface receptors that participate in the activation of T cells in response to the presentation of antigen. As for immunoglobulin molecules, the variable region of the alpha and beta chains are generated by V(D)J recombination, creating a large diversity of antigen specificities within the population of T cells. However, in contrast to immunoglobulins that recognize intact antigen, T cells are activated by processed peptide fragments in association with an MHC molecule, introducing an extra dimension to antigen recognition by T cells, known as MHC restriction. Recognition of MHC disparities between the donor and recipient through the T cell receptor leads to T cell proliferation and the potential development of GVHD. In order to effectively use allogeneic cells, the inactivation of TCRalpha or TCRbeta can result in the elimination of the TCR from the surface of T cells preventing recognition of alloantigen and thus GVHD.
On the other hand, host allogeneic cells can be rapidly rejected by the host immune system, a process termed host versus graft rejection (HvG) and this substantially limits the efficacy of the transferred cells. Allograft rejection is dependent upon recipient T lymphocytes responding to highly polymorphic cell surface molecules encoded by the MHC genes (the HLA system in humans). Although, the HLA immune response can be avoided by suppressing patient's immune system, the potency of allogeneic T cell engraftment from a single donor is influenced by the previous immunologic experience of the patient and the efficacy of engraftment is variable and not predictable. Indeed, patients who have been pregnant or who have had a blood transfusion may have already developed immunological memory and circulating antibodies to non-self HLA molecules and will, thus, be “sensitized” against certain HLA molecules. Thus, in general case of organ transplantation, graft rejection is triggered by anti-HLA antibodies. The graft rejection may be avoided by matching donor and recipient MHC (HLA) molecules. In practical terms, this has been managed 1) by performing a cell typing to determine the HLA genotype of donors and recipient prior engraftment, in order to select the closest HLA match and 2) by detecting circulating antibodies in the recipient's serum against HLA molecule on the donor lymphocytes. To avoid the typing of recipient T cells and the detection of circulating antibodies in the recipient's serum against HLA molecule on the donor's lymphocytes, the inventors propose for the first time to develop allogeneic immunotherapy product by generating batches of T cells originating from different donors.
The present method should allow obtaining a clinical response with averaged potency. Indeed, to avoid compromise of donor lymphocytes in patients with anti-HLA antibodies, lymphocytes selected to express varied HLA types are engrafted, thus preventing a high proportion of donor's cell to be subject to the same anti-HLA antibody. In addition, Natural Killer (NK) cells recognize HLA class I molecules via surface receptors killer immunoglobulin-like receptor (KIR) delivering signals that inhibit NK cell function. These receptors prevent NK cell-mediated attack against normal (i.e. HLAclass I+) autologous cells. Cells in which expression of HLA class I is different from autologous HLA become susceptible to NK-mediated killing.
The proper pooling of lymphocytes originating from different donors expressing varied HLA alleles, according to the invention, i.e. by taking into account variability among donors and patients, ensures that at least one fraction of the lymphocytes express appropriate MHC class I alleles that engage KIR and thus avoid a significant impact of NK alloreactivity on lymphocytes engraftment. In summary, the batch of lymphocytes originating from different donors minimizes impacts of existing anti-HLA immunoreactivity in patients, and reduces NK alloreactivity to allow clinical response with averaged potency.